Well, one of doing this (although I strongly recommend against this practise - not just this way, but using "names of variables" to get to the variables value in general) is:

use warnings;
use strict;
our $KPI0 = 10;
our $KPI1 = 20;
our $KPI2 = 30;
our $KPI3 = 40;
our $KPI4 = 50;
for (my $i = 0; $i < 5; $i++) {
    my $var = "KPI$i";
    no strict 'refs';
    print "line", $$var, "\n";
}
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But I can't imagine why you want it this way. Use an array or a hash:

use strict;
use warnings;
my @KPI = (10, 20, 30, 40, 50);
for (my $i = 0; $i < @KPI; $i++) {
    print "line", $KPI[$i], "\n";
}
[download]